The present invention relates to the transfer of a printed image onto a target substrate, especially poster board, foam board, or rigid PVC.
A wide variety of techniques have been developed for digitally capturing an image in the form of a computer-readable file, editing the image with a computer, printing the edited image onto a recording medium, and then transferring the image from the recording medium to a target substrate. A target substrate can be one of any number of materials including fabrics, ceramic materials, posterboard, rigid PVC, or mounting board such as, foam board or expanded PVC board which are widely used in the graphic art industry.
The typical recording medium for receiving and transferring an image formed by an ink-jet printer has a carrier and at least two of the following layers: a release layer, a protective barrier layer, image transfer layer, and an adhesive layer. The International Application PCT/GB98/00481 designating in the U.S., filed Feb. 16, 1998 for xe2x80x9cTransfer Filmxe2x80x9d (the disclosure of which is incorporated herein by reference), describes a carrier having a transfer film which has only one layer. This single layer is a mixture of heat-activatable adhesive particles and a binder that also is ink-absorbing, thereby defining a porous matrix. When used for commercial graphics applications, such a transfer film can be adhered to the target substrate without removing the carrier, whereby the carrier remains affixed to the layer holding the printed image, thereby providing physical protection for the image.
U.S. patent application Ser. No. 09/107,302 filed Jun. 30, 1998 for xe2x80x9cPrintable Laminatexe2x80x9d (the disclosure of which is incorporated herein by reference), describes a printable laminate material for transferring an image produced by an ink jet printer to a target substrate. The printable laminate has a carrier film on one side of which is disposed an image recording layer comprising an ink absorber and a heat activatable adhesive. The ink absorber is a modified cellulose material, though a cellulose gum or a single cationically charged water-soluble polymer may also be used. The heat activatable adhesive is a polyurethane. In the ""302 application the polyurethane of the image recording layer is in the form of small strand-like structures which are distributed throughout the ink absorber thereby forming an homogenous mixture with the ink absorber of the recording layer.
U.S. Pat. No. 5,501,902 describes a multi-layer printable transfer material which can be sealed at 177xc2x0 C. using a smoothing iron. However, this temperature is far too high for use with mounting boards commonly found in the graphic arts industry. Furthermore, the ""902 Patent describes the use of a powdered polymer with a particle size of up to 20xcexc. The large particle size tends to produce a printed image having a grainy appearance with a consequent loss of clarity, contrast and brilliance of the printed image.
International Patent Application WO 98/02314 describes a printable transfer material that releases from a temporary carrier, wherein the transferred image is waterproof. This material uses a porous matrix of large particles of a typical size of 20xcexc. The transfer material is subjected to a high temperature (typically 190xc2x0 C.) to form a film of polymer which encapsulates the ink inside the film.
The inventions disclosed in International Application PCT/GB98/00481 and U.S. patent application Ser. No. 09/107,302 have been further investigated, particularly regarding the ability of the printable laminate to resist the separation or delamination of the carrier film from the image recording layer. It was found that cutting or cropping of the printable laminate to obtain a proper size image for display or to obtain a mounted image having an irregular outline as found in some commercial advertising displays often causes the protective carrier layer to separate from the recording layer.
Separation of the carrier film under these circumstances appears to be due to shear, tension and compression forces exerted by the cutting blade during the cutting process. The forces build as the blade is drawn across and through the printable laminate and when the forces imposed in cutting the material are sufficient to overcome the adhesive yield point of the image transfer layer, the adhesive bond between the image recording layer and the carrier layer fails.
Upon failure, the carrier film separates from the image recording layer and the protection offered by the carrier layer is lost. Moreover, separation of the carrier layer can greatly detract from the quality of the printed image in that the separation may cause a xe2x80x9csilveringxe2x80x9d effect which may obscure the image or otherwise detract from the appearance of the image.
An object of the present invention is to provide a printable laminate material with improved resistance to delamination of the carrier film from the image recording layer through the use of new heat activated adhesives, new ink absorbers, and combinations thereof in the recording layer.
Another object of the present invention is to provide a printable laminate material having improved resistance to delamination of the carrier film provided by a layer of polymeric material having desirable viscoelastic properties in the structure of the printable laminate.
Other objects will be in part obvious and in part pointed out more in detail hereinafter.
These and related objects are achieved by providing in a first embodiment of the invention a printable laminate comprising a carrier film which is substantially transparent, and an image recording layer which is disposed on the carrier film. The image recording layer comprises a heat activated adhesive and an ink absorber. The heat activatable adhesive is one or more adhesive materials such as polyurethanes, vinyl ester copolymers, acrylics, and ionomers formed from various salts of olefins and unsaturated acid copolymers. The adhesives are most preferable those which are available in the form of aqueous dispersions. The ink absorber is one or more ink absorber materials such as blends of cationic polymers, blends of cationic polymers and cellulose ether, and polyvinyl alcohol. The new adhesives and combinations of adhesives and ink absorbers produce an ink recording layer with a higher yield point, making the laminate less susceptible to delamination.
According to a variation of the first embodiment, the printable laminate consists essentially of a substantially transparent carrier film having opposite first and second sides; a substantially uniform thermoplastic image recording layer having an inner surface directly supported by one side of the carrier film and an exposed outer surface for receiving printed ink; wherein a first, thermoplastic, heat activated adhesive material constitutes about 40-65 weight % of the recording layer, and at least 75 weight % of the remaining weight of the recording layer is constituted by a different, ink absorbing, thermoplastic, cationic polymer material.
In a second embodiment of the invention the printable laminate includes a carrier film which is substantially transparent, a layer of viscoelastic material disposed on the carrier film, and an image recording layer disposed on the layer of viscoelastic material. The viscoelastic material is one or more thermoplastic polymers such as polyurethanes, acrylics, vinyls, butadiene-styrene copolymers, isoprene-styrene copolymers, polychloroprenes, and olefinic polymers having physical properties which contribute to the xe2x80x9cdampingxe2x80x9d of shearing forces imposed by a blade cutting the laminate. The image recording layer includes an ink absorber which may be one or more blends of cationic polymers, blends of cationic polymers and cellulose ether, and polyvinyl alcohol, along with a heat activatable adhesive which may include one or more materials such as polyurethanes, vinyl ester copolymers, acrylic ester copolymers, and ionomers as previously described in reference to the heat activatable adhesives such as polyurethanes, phenoxy resins, acrylics, vinyls, butadiene-styrene copolymers, isoprene-styrene copolymers, polychloroprenes, and olefinic polymers, which may be the same or different than the viscoelastic materials as described herein above. The ink absorber in the image recording layer is the same as described in reference to the ink absorber of the first embodiment, namely one or more ink absorber materials such as blends of cationic polymers, blends of cationic polymers and cellulose ether, and polyvinyl alcohol.
The invention accordingly comprises the several components and the relation of one or more of such components with respect to each of the others, and the article possession of the features, properties, and relation of elements exemplified in the following detailed disclosure.